Sur le routeur R1, la passerelle à joindre est à l'adresse 10.1.30.2. Le code du script est téléchargeable à partir du lien suivant : r1-keepalive.sh.

#!/bin/bash

#* Adaptation d'un script publié par Lukas Ruf en 2006
#* License: GPL3

neighbor=10.1.30.2

scriptname=$(basename "$0")
scriptname=${scriptname%.*}
delay=10                              # sleep time
logfile=/var/log/${scriptname}.log    # file for debug messages
lockfile=/var/lock/${scriptname}.lock # locking to avoid races

# control where to log debug messages to:
# debugfile = 0 : log to /dev/null
# debugfile = 1 : log to file specified in ${logfile}
debugfile=1

# log a message to the log-file specified by debugfile
function keepalive_debug() {

        local msg="$1"
        local dat
        dat=$(date "+%b %d %H:%M:%S") # time stamp

        if [[ ${debugfile} == "1" ]]; then
                if lockfile -r 1 "${lockfile}"; then
                        touch "${logfile}" >/dev/null 2>&1
                        chmod 0644 "${logfile}" >/dev/null 2>&1
                        echo -n "${dat}: " >>"${logfile}" 2>&1
                        echo "${msg}" >>"${logfile}" 2>&1
                        rm -f "${lockfile}" >/dev/null 2>&1
                fi
        else
                echo "${msg}" >/dev/null 2>&1
        fi
}

# ping the ${neighbor} and sleep ${delay} seconds
function alive_ping() {

        local msg=""

        keepalive_debug "alive_ping"
        while true; do
                msg=$(/bin/ping -W 2 -n -c 1 "${neighbor}" 2>&1 | grep -E '(bytes from|100% packet loss)' || true)

                if [[ ${msg} =~ "bytes from" ]] && [[ ! -e /tmp/${neighbor}_up ]]; then
                        ip route add default via "${neighbor}"
                        touch /tmp/"${neighbor}"_up
                        keepalive_debug "${neighbor} is reachable, default route added"
                fi

                if [[ ${msg} =~ "100% packet loss" ]] && [[ -e /tmp/${neighbor}_up ]]; then
                        ip route del default via "${neighbor}"
                        rm -f /tmp/"${neighbor}"_up
                        keepalive_debug "${neighbor} is not reachable, default route deleted"
                fi

                sleep "${delay}"
        done
}

# start up and handle proper daemonization
function main() {

        local argument="daemon"

        if [[ $1 == "${argument}" ]]; then
                alive_ping
        else
                keepalive_debug "START"
                keepalive_debug "daemonize $0"
                nohup /bin/bash "$0" "${argument}" "$*" >/dev/null 2>&1 &
                keepalive_debug "daemonized $0"
        fi
}

main "$*"

exit 0

Sur le routeur R3, la passerelle à joindre est à l'adresse 10.1.30.10. Le code du script est téléchargeable à partir du lien suivant : r3-keepalive.sh.

Le code de ce script est identique au précédent à l'exception de la valeur attribuée à la variable ${neighbor}.